This invention relates to a switch mechanism and more particularly to a residual current device (RCD) incorporating the mechanism.
An RCD is a safety device which cuts power to an electrical appliance or other load in the event of certain faults. The device senses current imbalance between active and neutral power conductors resulting from earth currents created by the faults. A differential transformer generates an out of balance signal which is electronically amplified and compared with a predetermined threshold. Exceeding the threshold disables a switch mechanism and opens a contact set to cut the power. Several switch mechanisms are known but most are too expensive or bulky or otherwise unsuitable for general use.
Switches having a lever assembly which pivots about one or other of two fulcrums to open or close the contact set as in the present invention are disclosed in U.S. Pat. No. 4,010,431 Virani et-al, U.S. Pat. No. 4,034,266 Virani et-al, and U.S. Pat. No. 4,209,762 Samborski et-al. Reset is achieved in these cases however by pushing down on the close fulcrum rather than on the lever. In U.S. Pat. No. 3,813,579 Doyle et-al, a reset device pushes on the lever but also provides the open fulcrum rather than having independent pivot and reset action. In all of these cases a solenoid is energised to expel a plunger and trip the switch rather than being de-energised to simply release the plunger under bias from a spring. U.S. Pat. No. 4,567,456 Legatti, discloses a simple plunger release but there is no double pivoting action of a lever and the solenoid is required to maintain bending of a flexible arm. In each known case the plunger is restored by the solenoid itself or on reset, rather than almost immediately after release during pivoting of the lever.